pile_limit option - movement feedback "there are objects here" (trunk only)

Something that pops up in the newsgroup periodically, with <Someone>
inevitably pointing out the bit of code that the user needs to tweak,
about control of feedback when hero is walking across floor objects.
Implement new option ``pile_limit'' which allows user to set the point
at which the game switches from listing the objects to giving "there are
several/many objects here".  Default is 5, same as previous hard-coded
value (1 object gets listed via pline, 2..4 are listed in a corner popup,
5 or more objects yields a pline message instead).  Setting pile_limit
to 0 means no limit, so objects will always be listed regardless of pile
size.  Setting it to 1 effectively forces no listing since any non-empty
pile size is always at least that big, so can produce "there is an object
here" even though that's no briefer than a pline() to show one object.

doc/fixes35.0

@@ -323,6 +323,8 @@ player can give a monster class when asked for type of monster to poly into
 likewise when asked about type for #monpolycontrol
 scroll of taming/spell of charm monster now gives some feedback
 doppelgangers can take on the shape of alternate roles' quest guardians
+pile_limit option to control when to switch to "there are objects here"
+	vs listing objects on floor when hero goes over objects while moving
 
 
 Platform- and/or Interface-Specific New Features